Previously known, i.e., from Finnish patent application No. 895057, is a method of forcing tandem cylinders into soil by means of a hammer in the working pit. In the method, a conventional, non-rotatable hammer is used. The cylinders can only penetrate soft and granular soil, such as man-made road embankments.
Hammers are known as devices which direct the blows towards a tool while drivers are devices which drive the whole hammer in the direction of blow. Typically, these machines are used for working downwards, such that the hammer functions by means of gravity in all situations if operating in other directions, it is necessary to provide for a counterforce for the hammer so that there will be no stoppage because of dead travel.
In forcing cylinders into soil by means of a hammer, the first cylinder of which has the function of a tool, the disadvantage is that the forward movement stops if a large stone is hit, which cannot give way to the inside or outside of the cylinder. The forward movement can be stopped even by small rock walls which tend to change the direction if the cylinders are not rotated. The disadvantage of conventional hammers is the stopping of blows during operation. This is especially true at the first stage upon starting to force the cylinders into soil when they penetrate easily and there is no counterforce for the hammer, thereby causing the strokes to stop and disturb operation.